1. Field of the Invention
The present invention relates to an image forming apparatus, and more particularly to a technology for controlling the activation of devices connected to the image forming apparatus and/or devices installed in the image forming apparatus (internal devices).
2. Description of the Related Art
In recent years, image forming apparatuses typically referred to as Multi Function Peripherals (MFP) have become commonplace. In the MFP, multiple functions such as those of a printer, a copier, a fax machine, and a scanner are stored in a single body. In the MFP, a display unit, a printing unit, and an image forming unit are provided in a single body. Furthermore, software corresponding to a printer, a copier, and a fax machine is installed in the MFP. By switching among these software items, the MFP can operate as a printer, a copier, a fax machine, and a scanner.
When such a conventional MFP is activated by turning on the main power supply, a controller that controls the operation of activating devices (engines) needs to be activated before each of the devices (engines) can be activated. For this reason, the time required for activating the entire MFP depends on the time required for activating the controller.
In the technology proposed in patent document 1, before establishing communications between the controller and the engines, a hard line (information transmission unit) can acquire information indicating whether the image forming apparatus has started up by turning on the main power supply or whether the image forming apparatus has returned from a power-saving mode. Accordingly, the engines can be activated without waiting for the controller to be activated, so that the time required for activating connected devices and/or internal devices can be reduced.    Patent Document 1: Japanese Laid-Open Patent Application No. 2007-301765
However, in the conventional image forming apparatus disclosed in patent document 1, the connected devices and/or the internal devices are activated at the same time. Thus, in some cases, the power consumed when activating the devices may exceed the maximum usable power of the power supply unit.
When the power consumed when activating the devices exceeds the maximum usable power, the power cannot be stably supplied to the devices. As a result, the state of the image forming apparatus becomes unstable.
Accordingly, the image forming apparatus needs to control the process of activating the devices (activation control), so that the power consumed when activating the devices does not exceed the maximum usable power.
When performing activation control, it is necessary to consider the number of connected devices, the connection pattern, and the activating properties of the devices. These factors significantly affect power consumption. Therefore, in order to control the power consumption and the activation standby time (time taken for activation), it is important to adjust the timing of issuing triggers (control signals) for instructing activation of the devices, i.e., the timing of activating the plural devices.
An image forming apparatus is typically provided with one type of power source unit. However, different image forming apparatuses may have various configurations. In one example, the power consumption may not exceed the maximum usable power even when the connected devices, the scanner (scanning device), the image forming unit (image forming device), and the fixing unit are activated at the same time. In this example, the image forming apparatus may be overengineered due to the power supply unit. In the same manner as selecting other devices, it would be preferable to select a power supply unit that supplies an appropriate amount of power in accordance with the configuration of the image forming apparatus (power supply required for stable operations).